Thermoset polyurethanes based on moisture-resistant polyols for use in golf balls

ABSTRACT

The present invention provides golf balls having a rubber core, and a cover layer made from a thermoset polyurethane of polyurethane-urea that is the reaction product of a polyisocyanate with moisture-resistant polyol and curing agent. An intermediate layer, formed from an olefin-based acid copolymer ionomer composition and preferably an ethylene acid copolymer, is disposed between the rubber core and cover. The moisture-resistant polyol is preferably a reaction product of dimer acid or dimer ester and a polyolefin diol, or a polybutadiene polyol, or a polyisoprene. Preferably, the cover layer has a moisture vapor transmission rate (MVTR) between 3 grams·mm/m 2 ·day to 4 grams·mm/m 2 ·day.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, co assigned U.S. patentapplication Ser. No. 12/762,410 having a filing date of Apr. 19, 2010,now issued as U.S. Pat. No. 8,524,852 with an issue date of Sep. 3,2013, the entire disclosure of which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to golf balls containing atleast one layer made from a thermoset polyurethane or polyurethane-ureacomposition that is based on a moisture-resistant polyol. Moreparticularly, the composition is produced from a reaction ofpolyisocyanate with a moisture-resistant polyol and curing agent. Thecomposition may be used to form any layer in the golf ball such as, forexample, an outer core, intermediate layer, inner cover, and/or outercover. The resulting golf ball has desirable playing performanceproperties including high resiliency, toughness, impact durability,moisture-resistance, and soft feel.

2. Brief Review of the Related Art

Today, multi-piece solid golf balls are popular for several reasonsincluding new manufacturing methods, the availability and cost of rawmaterials, and the playing performance properties of such balls. Forexample, three-piece solid golf balls having an inner core and outercover with an intermediate layer disposed there between are commonlyused by both professional and recreational golfers. Many multi-pieceballs are designed to have an optimum combination of playing properties.Particularly, such balls are designed to have high durability andresiliency as well as a soft feel. The durability and toughness of theball protects it from being cut, torn, and otherwise damaged. Ballshaving a high resiliency tend to reach a high velocity when struck by agolf club. As a result, the ball tends to travel a greater distancewhich is particularly important for driver shots off the tee. Meanwhile,the soft feel of the ball provides the player with a more pleasantsensation when he/she strikes the ball with the club. The player sensesmore control over the ball as the club face makes impact. The soft feelof the ball's cover allows players to place a spin on the ball andbetter control its flight pattern which is particularly important forapproach shots near the green.

In conventional multi-piece golf balls, the inner core is made commonlyof a rubber material such as natural and synthetic rubbers, styrenebutadiene, polybutadiene, poly(cis-isoprene), poly(trans-isoprene), orhighly neutralized acid copolymers. Often, the intermediate layer ismade of an olefin-based ionomer resin that imparts some hardness to theball. These ionomer acid copolymers contain inter-chain ionic bondingand are generally made of an α-olefin such as ethylene and a vinylcomonomer having an acid group such as methacrylic, acrylic acid, ormaleic acid. Metal ions such as sodium, lithium, zinc, and magnesium areused to neutralize the acid groups in the copolymer. Commerciallyavailable olefin-based copolymer ionomer resins are used in differentindustries and include numerous resins sold under the trademarks,Surlyn® (available from DuPont) and Escor® and Iotek® (available fromExxonMobil), Amplify IO® (available from Dow Chemical) and Clarix®(available from A. Schulman). Olefin-based copolymer ionomer resins areavailable in various grades and identified based on the type of baseresin, molecular weight, and type of metal ion, amount of acid, degreeof neutralization, additives, and other properties. Finally, the outercover of conventional golf balls are made from a variety of materialsincluding olefin-based copolymer ionomers, polyamides, polyesters, andthermoplastic and thermoset polyurethane and polyurea elastomers.

In recent years, there has been substantial interest in using thermosetand thermoplastic polyurethanes to make cover layers for the golf balls.Polyurethane golf ball covers are of particular interest because theycan be formulated to provide the golf ball with high resiliency anddurability as well as a soft feel. Basically, polyurethane compositionscontain urethane linkages formed by reacting an isocyanate group(—N═C═O) with a hydroxyl group (OH). Polyurethanes are produced by thereaction of a polyisocyanate with a polyol in the presence of a catalystand other additives. The chain length of the polyurethane prepolymer isextended by reacting it with a hydroxyl-terminated curing agent. Hybridcompositions containing urethane and urea linkages also may be produced.For example, a polyurethane/urea hybrid composition may be produced whenpolyurethane prepolymer is reacted with an amine-terminated curingagent.

Golf balls made with polyurethane and polyurea materials are generallydescribed in the patent literature, for example, U.S. Pat. Nos.5,334,673; 5,484,870; 6,476,176; 6,506,851; 6,867,279; 6,958,379;6,960,630; 6,964,621; 7,041,769; 7,105,623; 7,131,915; and 7,186,777. Asdiscussed above, in general, isocyanate compounds with two or morefunctional groups are reacted with polyols to form the polyurethanecompositions. There are various known methods for making thermoplasticpolyurethanes. For example, Meltzer et al., U.S. Patent ApplicationPublication No. US 2009/0192262 describes a specific method for makinghydrophobic thermoplastic polyurethanes. According to the '262Publication, a polyol, a polyisocyanate, and a linear diol chainextender containing 5 carbon atoms or 7 to 12 carbon atoms are requiredas the reactants. There is no disclosure of isocyanate or polyolcompounds containing acidic or ionic moieties. The '262 Publicationdiscloses that the thermoplastic polyurethane compositions may be usedfor over-molding soft grips onto tools and kitchen utensils, and inadhesives and protective coatings.

Although many conventional golf balls containing polyurethane componentsor layers have good mechanical and playing properties, there is acontinuing need for improved polyurethane golf balls. The improved golfballs should have high resiliency, impact durability, and toughness aswell as features that make the ball easy to play with, particularly apleasant feel, softness, and the like. The present invention providesmethods for making such golf balls and the resultant balls. The presentinvention relates to multi-layered golf balls made from a compositioncomprising a thermoset polyurethane or polyurethane-urea. Thecomposition may be used to form any layer in the golf ball structuresuch as, for example, outer core, intermediate layer, inner cover,and/or outer cover. The golf balls made of the compositions of thisinvention are highly resilient and have good impact durability andtoughness. Moreover, the ball has a soft feel and optimum playingperformance properties.

SUMMARY OF THE INVENTION

The present invention relates to multi-layered golf balls made from acomposition comprising a thermoset polyurethane or polyurethane-ureathat is based on a moisture-resistant polyol. The thermoset compositionpreferably has a cross-link density in the range of about 10 to about300 mol/m³ and a Vicat softening temperature in the range of about 60°to about 180° C. More particularly, the composition is formed from: i)an isocyanate compound, ii) a moisture-resistant polyol having a weightaverage molecular weight in the range of 500 to 10,000 grams per mole,and iii) a curing agent. The composition may be used to form any layerin the golf ball structure such as for example, outer core, intermediatelayer, inner cover, and/or outer cover. The golf balls made of thecomposition of this invention are highly resilient and have good impactdurability and toughness. The composition provides the golf ball withgood moisture-resistance. Moreover, the ball's cover has a soft feel andthe ball has optimum playing performance properties.

In one preferred embodiment, the ball includes a core which can be madeof polybutadiene, highly neutralized polymer, or other suitablematerial. The core preferably has a Shore C surface hardness in therange of about 50 to about 90. An intermediate layer comprising athermoplastic or thermoset composition surrounds the core. One exampleof a suitable thermoplastic composition that can be used to form theintermediate layer is an ethylene-based copolymer ionomer. A covercomprising the thermoset polyurethane or polyurethane-urea compositionof this invention surrounds the intermediate layer, and the cover has aShore C surface hardness in the range of about 60 to about 95. Thisthermoset cover composition is the reaction product of: i) an isocyanatecompound, ii) a moisture-resistant polyol having a weight averagemolecular weight in the range of 500 to 10,000 grams per mole, and iii)a curing agent selected from hydroxyl-terminated or amine-terminatedcuring agents, and mixtures thereof. The resulting thermoset compositionpreferably has a cross-link density in the range of about 10 to about300 mol/m³ and a Vicat softening temperature in the range of about 60°to about 180° C. In one preferred embodiment, the core has a diameter ofabout 1.26 to about 1.60 inches and surface hardness of about 30 toabout 65 Shore D; the intermediate layer has a thickness of about 0.015to about 0.120 inches and surface hardness of about 45 to about 75 ShoreD; and the cover layer has a thickness of about 0.015 to about 0.090inches and material hardness of about 40 to about 65 Shore D.

Different moisture-resistant polyols may be used. For instance, themoisture-resistant polyol may be the reaction product of dimer acid ordimer ester and a polyolefin diol, polybutadiene polyol, or polyisoprenediol. In one example, the polybutadiene polyol or polyisoprene diol arehydrogenated. In yet another version, a polyether-ester diol, which isthe reaction product of dimer acid or dimer ester and polyether diol, isused. A polycaprolactone-ester diol, which is the reaction product ofdimer acid or dimer ester and polycaprolactone diol, also may be used.The moisture-resistant polyol may be prepared by dimerizing unsaturatedaliphatic monocarboxylic acid or ester containing 10 to 60 carbon atomsfollowed by reacting it with a monomeric or polymeric diol. In onepreferred version, the moisture-resistant polyol is a branched polyesterpolyol containing 36 carbon atoms.

In a second preferred embodiment, the ball includes a core having aShore C surface hardness in the range of about 60 to about 95. Anintermediate layer comprising a thermoplastic or thermoset compositionsurrounds the core. One example of a suitable thermoplastic compositionthat can be used to form the intermediate layer is an ethylene-basedcopolymer ionomer. A multi-layered cover with inner and outer coverlayers comprising the polyurethane or polyurethane-urea composition ofthis invention surrounds the intermediate layer, and the cover has aShore C surface hardness in the range of about 50 to about 90.

Preferably, the thermoset polyurethane or polyurethane-urea polymercomposition has a Vicat softening temperature of 60° to 180° C., andmaterial Shore D hardness of about 30 to about 75. The thermosetpolyurethane or polyurethane-urea composition is post cross-linked usinga chemical or radiation cross-linking process. In one version, thereaction used to produce the thermoset polyurethane or polyurethane-ureacomposition is a one-step reaction. In a second version, the reactionused to produce the thermoset polyurethane or polyurethane-ureacomposition is a two-step reaction, wherein the first step comprisesreacting the isocyanate compound and moisture-resistant polyol to form aprepolymer and the second step comprises reacting the prepolymer withthe curing agent.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a front view of a dimpled golf ball made in accordance withthe present invention;

FIG. 2 is a cross-sectional view of a multi-layered (three-piece) golfball having an intermediate layer made of a polyurethane composition inaccordance with the present invention;

FIG. 3 is a cross-sectional view of a multi-layered (four-piece) golfball having an outer core layer made of a polyurethane composition inaccordance with the present invention;

FIG. 4 is a cross-sectional view of a multi-layered (four-piece) golfball having an inner cover layer made of a polyurethane composition inaccordance with the present invention; and

FIG. 5 is a cross-sectional view of a multi-layered (five-piece) golfball having a multi-layered core, intermediate layer, and outer coverlayer made in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates generally to golf balls containing atleast one “layer” made from a thermoset polyurethane orpolyurethane-urea composition that is produced by a reaction of: i) anisocyanate compound, ii) a moisture-resistant polyol having an averagemolecular weight in the range of 500 to 10,000 grams per mole and ahydroxyl value in the range of 30 to 120, and iii) a curing agentselected from hydroxyl-terminated and amine-terminated curing agents andmixtures thereof. The term, “layer” as used herein means generally anyspherical portion of a golf ball. The polyurethane or polyurethane-ureacomposition of this invention may be used to form any layer in the golfball structure including, but not limited to, an outer cover, innercover, intermediate layer, and/or outer core layer.

Isocyanate Compounds

Any suitable isocyanate known in the art can be used to produce thepolyurethane composition in accordance with this invention. Suchisocyanates include, for example, aliphatic, cycloaliphatic, aromaticaliphatic, aromatic, any derivatives thereof, and combinations of thesecompounds having two or more isocyanate (—N═C═O) groups per molecule.The isocyanates may be organic polyisocyanate-terminated prepolymers,isocyanate prepolymers having a low residual amount of unreactedisocyanate monomer (“low free” isocyanates), and mixtures thereof. Theisocyanate-containing reactable component also may include anyisocyanate-functional monomer, dimer, trimer, or polymeric adductthereof, prepolymer, quasi-prepolymer, or mixtures thereof.Isocyanate-functional compounds may include monoisocyanates orpolyisocyanates that include any isocyanate functionality of two ormore.

Preferred isocyanates include diisocyanates (having two NCO groups permolecule), biurets thereof, dimerized uretdiones thereof, trimerizedisocyanurates thereof, and polyfunctional isocyanates such as monomerictriisocyanates. Diisocyanates typically have the generic structure ofOCN—R—NCO. Exemplary diisocyanates include, but are not limited to,unsaturated isocyanates such as: p-phenylene diisocyanate (“PPDI,” i.e.,1,4-phenylene diisocyanate), m-phenylene diisocyanate (“MPDI,” i.e.,1,3-phenylene diisocyanate), o-phenylene diisocyanate (i.e.,1,2-phenylene diisocyanate), 4-chloro-1,3-phenylene diisocyanate,toluene diisocyanate (“TDI”), m-tetramethylxylene diisocyanate(“m-TMXDI”), p-tetramethylxylene diisocyanate (“p-TMXDI”), 1,2-, 1,3-,and 1,4-xylene diisocyanates, 2,2′-, 2,4′-, and 4,4′-biphenylenediisocyanates, 3,3′-dimethyl-4,4′-biphenylene diisocyanate (“TODI”),2,2′-, 2,4′-, and 4,4′-diphenylmethane diisocyanates (“MDI”),3,3′-dimethyl-4,4′-diphenylmethane diisocyanate, carbodiimide-modifiedMDI, polyphenylene polymethylene polyisocyanate (“PMDI,” i.e., polymericMDI), 1,5-naphthalene diisocyanate (“NDI”), 1,5-tetrahydronaphththalenediisocyanate, anthracene diisocyanate, tetracene diisocyanate; andsaturated isocyanates such as: 1,4-tetramethylene diisocyanate,1,5-pentamethylene diisocyanate, 2-methyl-1,5-pentamethylenediisocyanate, 1,6-hexamethylene diisocyanate (“HDI”) and isomersthereof, 2,2,4- and 2,4,4-trimethylhexamethylene diisocyanates,1,7-heptamethylene diisocyanate and isomers thereof, 1,8-octamethylenediisocyanate and isomers thereof, 1,9-nonamethylene diisocyanate andisomers thereof, 1,10-decamethylene diisocyanate and isomers thereof,1,12-dodecane diisocyanate and isomer thereof, 1,3-cyclobutanediisocyanate, 1,2-, 1,3-, and 1,4-cyclohexane diisocyanates, 2,4- and2,6-methylcyclohexane diisocyanates, isophorone diisocyanate (“IPDI”),isocyanatomethylcyclohexane isocyanate, isocyanatoethylcyclohexaneisocyanate, 4,4′-dicyclohexylmethane diisocyanate (“H₁₂ MDI,” i.e.,bis(4-isocyanatocyclohexyl)-methane), and 2,4′- and 4,4′-dicyclohexanediisocyanates. Dimerized uretdiones of diisocyanates and polyisocyanatesinclude, for example, unsaturated isocyanates such as uretdiones oftoluene diisocyanates, uretdiones of diphenylmethane diisocyanates; andsaturated isocyanates such as uretdiones of hexamethylene diisocyanates.Trimerized isocyanurates of diisocyanates and polyisocyanates include,for example, unsaturated isocyanates such as trimers of diphenylmethanediisocyanate, trimers of tetramethylxylene diisocyanate, isocyanuratesof toluene diisocyanates; and saturated isocyanates such asisocyanurates of isophorone diisocyanate, isocyanurates of hexamethylenediisocyanate, isocyanurates of trimethyl-hexamethylene diisocyanates.Monomeric triisocyanates include, for example, unsaturated isocyanatessuch as 2,4,4′-diphenylene triisocyanate, 2,4,4′-diphenylmethanetriisocyanate, 4,4′,4″-triphenylmethane triisocyanate; and saturatedisocyanates such as: 1,3,5-cyclohexane triisocyanate.

Other suitable isocyanates include acid functionalized isocyanatescontaining acid groups such as, for example, carboxylic, sulfonic, orphosphoric acid groups. The acid content may be, for example, in therange of about 2.5 wt. % to about 25 wt. %, preferably about 5 to about20 wt. %, based on weight of polymer composition. Also, the acid groupsof the acid-functionalized isocyanates may be partially, highly, orfully neutralized using organic or inorganic cations to form ionomers.For example, the neutralization level may be from 10 to 80%, morepreferably 20 to 70%, and most preferably 30 to 50% forpartially-neutralized ionomers. In another embodiment, theneutralization level is from 80 to 100%, more preferably 90 to 100%, andmost preferably 95 to 100% for highly or fully-neutralized ionomers. Byincorporating acid or ionic groups into the backbone of the isocyanates,the properties of the resulting polyurethane such asscuff/abrasion-resistance and resiliency can be enhanced.

Preferably, the isocyanate compound is selected from the groupconsisting of monomeric, oligomeric, or polymeric isophoronediisocyanate (IPDI); hexamethylene diisocyanate (HDI); 1,4-cyclohexyldiisocyanate (CHDI); 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI);4,4′-dicyclohexylmethane diisocyanate (4,4′-MDI); 4,4′-diphenylmethanediisocyanate (“MDI”); toluene diisocyanate (TDI); p-phenylenediisocyanate (PPDI); 1,5-naphthalene diisocyanate (“NDI”); xylenediisocyanate (“XDI”); and tetramethylxylene diisocyanate (TMXDI”); andmixtures thereof.

Polyol Compounds

As discussed above, a polyurethane composition is generally anelastomeric material that is the reaction product of isocyanate andhydroxyl components. There are many polyol compounds known in the art.Surprisingly, it has been found that a moisture-resistant polyol that isthe reaction of product of a dimer acid or dimer ester and a polyolefindiol, polybutadiene polyol, or polyisoprene diol is particularlyeffective and provides a polyurethane composition having manyadvantageous properties for purposes of this invention. For instance,because of the moisture-resistant polyols, the resulting polyurethanecompositions of this invention will tend to have greatermoisture-resistance than polyurethane compositions prepared from polyolsthat are not highly moisture-resistant. In a second preferredembodiment, the dimer acid or dimer ester is reacted with ahydrogentated polybutadiene or hydrogenated polyisoprene diol to producea moisture-resistant polyol that, in turn, can be reacted with theisocyanate compound to produce the polyurethane composition. Anotherpreferred moisture-resistant polyol that can be used in this inventionis a polyether-ester diol that is the reaction product of a dimer acidor dimer ester and a polyether diol. In yet another preferred version,the moisture-resistant polyol is a polycaprolactone-ester diol that isthe reaction product of a dimer acid and polycaprolactone diol.

Other suitable polyols include acid functionalized polyols containingacid groups such as, for example, carboxylic, sulfonic, or phosphoricacid groups. The acid content may be, for example, in the range of about2.5 wt. % to about 25 wt. %, preferably about 5 to about 20 wt. %, basedon weight of polymer composition. Also, the acid groups of theacid-functionalized polyols may be partially, highly, or fullyneutralized using organic or inorganic cations to form ionomers. Forexample, the neutralization level may be from 10 to 80%, more preferably20 to 70%, and most preferably 30 to 50% for partially-neutralizedionomers. In another embodiment, the neutralization level is from 80 to100%, more preferably 90 to 100%, and most preferably 95 to 100% forhighly or fully-neutralized ionomers. By incorporating acid or ionicgroups into the backbone of the polyols, the properties of the resultingpolyurethane such as tensile strength, impact durability, resiliency,and toughness can be enhanced. Mixtures of the above-describedmoisture-resistant polyols also can be used in accordance with thisinvention.

Dimer acids and dimer esters are commercially available and can be usedto prepare the moisture-resistant polyols of this invention. They arenormally prepared by dimerizing unsaturated long chain aliphaticmonocarboxylic acids, usually of 10 to 60 carbon atoms, or their esters(alkyl esters). This is followed by reacting the dimer acid or dimerester with a monomeric or polymeric polyol. Certain moisture-resistantpolyols are commercially available and can be used in accordance withthis invention. For example, Priplast™ olyester polyols, available fromUniqema of Gouda (The Netherlands) are branched C₃₆ moisture-resistantpolyols that can be used. The moisture-resistant polyol used insynthesizing the thermoset polyurethane of this invention typically willhave a weight average molecular weight in the range of about 500 toabout 10,000 grams per mole and preferably will have a hydroxyl value inthe range of 30 to 120 mg KOH/g (as measured in accordance with ASTME-222). The moisture-resistant polyols used in this invention have highhydrolytic resistance and tensile strength. Thus, they can be reactedwith isocyanate compounds and curing agents to produce polyurethanecompositions having ideal properties as discussed further below.Moreover, the moisture-resistant polyols have a highlymoisture-resistant backbone. Thus, the resulting polyurethanescompositions will tend to be more moisture-resistant than polyurethanesprepared from polyols that do not have a moisture-resistant backbone.

Manufacturing Processes

There are two basic techniques that can be used to make the polyurethanecompositions of this invention: a) one-shot technique, and b) prepolymertechnique. In the one-shot technique, the isocyanate, polyol, andhydroxyl and/or amine-terminated curing agent are reacted in one step.The prepolymer technique involves a first reaction between theisocyanate and polyol compounds to produce a polyurethane prepolymer,and a subsequent reaction between the prepolymer and hydroxyl and/oramine-terminated curing agent. As a result of the reaction between theisocyanate and polyol compounds, there will be some unreacted NCO groupsin the polyurethane prepolymer. The prepolymer should have less than 14%unreacted NCO groups. Preferably, the prepolymer has no greater than8.5% unreacted NCO groups, more preferably from 2.5% to 8%, and mostpreferably from 5.0% to 8.0% unreacted NCO groups. As the weight percentof unreacted isocyanate groups increases, the hardness of thecomposition also generally increases.

Either the one-shot or prepolymer method may be employed to produce thethermoset polyurethane compositions of the invention. In one embodiment,the one-shot method is used, wherein the isocyanate compound is added toa reaction vessel and then a curative mixture comprising the polyol andcuring agent is added to the reaction vessel. The components are mixedtogether so that the molar ratio of isocyanate compound to total polyoland curing agent compounds is in the range of about 1.01:1.00 to about1.10:1.00. Preferably, the molar ratio is greater than 1.05:1.00. Forexample, the molar ratio can be in the range of 1.07:1.00 to 1.10:1.00.In general, the prepolymer technique is preferred because it providesbetter control of the chemical reaction. The prepolymer method providesa more homogeneous mixture resulting in a more consistent polymercomposition. In one embodiment, the prepolymer method is used, whereinthe isocyanate and polyol compounds are reacted to produce apolyurethane prepolymer. This is followed by a reaction between theprepolymer and curing agent to form the final polymer composition. Inthe prepolymer method, the prepolymer is mixed with the curing agent sothat the molar ratio of isocyanate groups to hydroxyl groups (and/oramine groups) is in the range of about 1.01:1.00 to about 1.10:1.00.Preferably, the molar ratio is greater than 1.05:1.00. For example, themolar ratio can be in the range of 1.07:1.00 to 1.10:1.00.

The resulting polyurethane prepolymer contains urethane linkages havingthe following general structure:

where x is the chain length, i.e., about 1 or greater, and R and R₁ arestraight chain or branched hydrocarbon chain having about 1 to about 20carbons

In general, polyurethanes are classified as either thermoplastic orthermosetting materials. Thermoplastic polyurethanes have somecross-linking, but it is primarily through hydrogen bonding or otherphysical mechanism. Because of their lower level of cross-linking,thermoplastic polyurethanes are relatively flexible. The cross-linkingbonds in thermoplastic polyurethanes can be reversibly broken byincreasing temperature such as during molding or extrusion. That is, thetheremoplastic material softens when exposed to heat and returns to itsoriginal condition when cooled. On the other hand, thermosetpolyurethanes become irreversibly set when they are cured. Thecross-linking bonds are irreversibly set and are not broken when exposedto heat. Thus, thermoset polyurethanes, which typically have a highlevel of cross-linking, are relatively rigid.

Chain-Extending of Prepolymer

As discussed above, either the one-shot or prepolymer method may be usedto form the thermoset polyurethane composition. In the prepolymermethod, the polyurethane prepolymer can be chain-extended by reacting itwith a single curing agent or blend of curing agents. In general, theprepolymer can be reacted with hydroxyl-terminated curing agents,amine-terminated curing agents, or mixtures thereof. The curing agentsextend the chain length of the prepolymer and build-up its molecularweight. The compositions of the present invention are castable thermosetpolyurethane materials.

A catalyst may be employed to promote the reaction between theisocyanate and polyol compounds for producing the prepolymer or betweenprepolymer and curing agent during the chain-extending step. Preferably,the catalyst is added to the reactants before producing the prepolymer.Suitable catalysts include, but are not limited to, bismuth catalyst;zinc octoate; stannous octoate; tin catalysts such as bis-butyltindilaurate, bis-butyltin diacetate, stannous octoate; tin (II) chloride,tin (IV) chloride, bis-butyltin dimethoxide,dimethyl-bis[1-oxonedecyl)oxy]stannane, di-n-octyltin bis-isooctylmercaptoacetate; amine catalysts such as triethylenediamine,triethylamine, and tributylamine; organic acids such as oleic acid andacetic acid; delayed catalysts; and mixtures thereof. The catalyst ispreferably added in an amount sufficient to catalyze the reaction of thecomponents in the reactive mixture. In one embodiment, the catalyst ispresent in an amount from about 0.001 percent to about 1 percent, andpreferably 0.1 to 0.5 percent, by weight of the composition.

The hydroxyl-terminated chain-extending (curing) agents are preferablyselected from the group consisting of ethylene glycol; diethyleneglycol; polyethylene glycol; propylene glycol; 2-methyl-1,3-propanediol;2-methyl-1,4-butanediol; monoethanolamine; diethanolamine;triethanolamine; monoisopropanolamine; diisopropanolamine; dipropyleneglycol; 1,2-butanediol; 1,3-butanediol; 1,4-butanediol; 2,3-butanediol;2,3-dimethyl-2,3-butanediol; trimethylolpropane; cyclohexyldimethylol;triisopropanolamine; N,N,N′,N′-tetra-(2-hydroxypropyl)-ethylene diamine;diethylene glycol bis-(aminopropyl) ether; 1,5-pentanediol;1,6-hexanediol; 1,3-bis-(2-hydroxyethoxy) cyclohexane;1,4-cyclohexyldimethylol; 1,3-bis-[2-(2-hydroxyethoxy)ethoxy]cyclohexane; 1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}cyclohexane; trimethylolpropane; polytetramethylene etherglycol (PTMEG), preferably having a molecular weight from about 250 toabout 3900; and mixtures thereof. In addition, the followinghydroxyl-terminated curing agents may be used: 1,7-heptanediol,1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and1,12-dodecanediol. However, it is not required that only linearhydroxyl-terminated curing agents containing 1 to 12 carbon atoms beused in the method of this invention. For instance, linearhydroxyl-terminated curing agents containing greater than 12 carbonatoms such as tetradecanoic (C₁₄) diols, hexadecanoic (C₁₆) diols, andoctadecanoic (C₁₈) diols may be used. In addition, alkyl or arylsubstituted alkane diols containing greater than 12 carbon atoms may beused. As discussed above, the properties of the polyurethane compositiondepend in significant part upon the components or building blocks usedto make the composition, particularly the polyisocyanates,moisture-resistant polyols, and curing agents of this invention. Theabove-mentioned hydroxyl-terminated curing agents may be used to makepolyurethane compositions having enhanced tensile strength, impactdurability, scuff/abrasion-resistance, resiliency, as well asmoisture-resistance.

Suitable amine-terminated chain-extending (curing) agents that can beused in chain-extending the polyurethane prepolymer of this inventioninclude, but are not limited to, unsaturated diamines such as4,4′-diamino-diphenylmethane (i.e., 4,4′-methylene-dianiline or “MDA”),m-phenylenediamine, p-phenylenediamine, 1,2- or1,4-bis(sec-butylamino)benzene, 3,5-diethyl-(2,4- or 2,6-)toluenediamine or “DETDA”, 3,5-dimethylthio-(2,4- or 2,6-)toluenediamine, 3,5-diethylthio-(2,4- or 2,6-)toluenediamine,3,3′-dimethyl-4,4′-diamino-diphenylmethane,3,3′-diethyl-5,5′-dimethyl4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-ethyl-6-methyl-benezeneamine)),3,3′-dichloro-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-chloroaniline) or “MOCA”),3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaniline),2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(3-chloro-2,6-diethyleneaniline) or “MCDEA”),3,3′-diethyl-5,5′-dichloro-4,4′-diamino-diphenylmethane, or “MDEA”),3,3′-dichloro-2,2′,6,6′-tetraethyl-4,4′-diamino-diphenylmethane,3,3′-dichloro-4,4′-diamino-diphenylmethane,4,4′-methylene-bis(2,3-dichloroaniline) (i.e.,2,2′,3,3′-tetrachloro-4,4′-diamino-diphenylmethane or “MDCA”),4,4′-bis(sec-butylamino)-diphenylmethane,N,N′-dialkylamino-diphenylmethane,trimethyleneglycol-di(p-aminobenzoate),polyethyleneglycol-di(p-aminobenzoate),polytetramethyleneglycol-di(p-aminobenzoate); saturated diamines such asethylene diamine, 1,3-propylene diamine, 2-methyl-pentamethylenediamine, hexamethylene diamine, 2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine, imino-bis(propylamine), imido-bis(propylamine),methylimino-bis(propylamine) (i.e.,N-(3-aminopropyl)-N-methyl-1,3-propanediamine),1,4-bis(3-aminopropoxy)butane (i.e.,3,3′-[1,4-butanediylbis-(oxy)bis]-1-propanamine),diethyleneglycol-bis(propylamine) (i.e.,diethyleneglycol-di(aminopropyl)ether),4,7,10-trioxatridecane-1,13-diamine, 1-methyl-2,6-diamino-cyclohexane,1,4-diamino-cyclohexane, poly(oxyethylene-oxypropylene) diamines, 1,3-or 1,4-bis(methylamino)-cyclohexane, isophorone diamine, 1,2- or1,4-bis(sec-butylamino)-cyclohexane, N,N′-diisopropyl-isophoronediamine, 4,4′-diamino-dicyclohexylmethane,3,3′-dimethyl-4,4′-diamino-dicyclohexylmethane,3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,N,N′-dialkylamino-dicyclohexylmethane, polyoxyethylene diamines,3,3′-diethyl-5,5′-dimethyl-4,4′-diamino-dicyclohexylmethane,polyoxypropylene diamines,3,3′-diethyl-5,5′-dichloro-4,4′-diamino-dicyclohexylmethane,polytetramethylene ether diamines,3,3′,5,5′-tetraethyl-4,4′-diamino-dicyclohexylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaminocyclohexane)),3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-dicyclohexylmethane,(ethylene oxide)-capped polyoxypropylene ether diamines,2,2′,3,3′-tetrachloro-4,4′-diamino-dicyclohexylmethane,4,4′-bis(sec-butylamino)-dicyclohexylmethane; triamines such asdiethylene triamine, dipropylene triamine, (propylene oxide)-basedtriamines (i.e., polyoxypropylene triamines),N-(2-aminoethyl)-1,3-propylenediamine (i.e., N₃-amine), glycerin-basedtriamines, (all saturated); tetramines such asN,N′-bis(3-aminopropyl)ethylene diamine (i.e., N₄-amine) (bothsaturated), triethylene tetramine; and other polyamines such astetraethylene pentamine (also saturated). The amine curing agents usedas chain extenders normally have a cyclic structure and a low molecularweight (250 or less). More preferably, the amine-terminated curing agentcan be selected from the group consisting of: 1,3-propane diamine,1,4-butane diamine, 1,5-pentane diamine, 1,6-hexane diamine, 1,7-heptanediamine, 1,8-octane diamine, 1,9-nonane diamine, 1,10-decane diamine,1,11-undecane diamine, and 1,12-docdeane diamine,polymethylene-di-p-aminobenzoates,polyethyleneglycol-bis(4-aminobenzoates), polytetramethyleneetherglycol-di-p-aminobenzoate, polypropyleneglycol-di-p-aminobenzoate,and mixtures thereof.

In yet other embodiment, a polyamide curing agent having multiple aminogroups capable of reacting with the isocyanate groups and at least oneamide group can be used. Polyamine polyamides can be used, wherein thepolyamide chain is formed from condensation polymerization reaction ofpolyacid (including polyacid telechelic) and polyamine (includingpolyamine telechelic), with an equivalent ratio of polyamine to polyacidbeing greater than 1, such as about 1.1-5 or about 2. Mixtures ofpolyacid and polyamine can be, for example, hexamethylene diammoniumadipate, hexamethylenediammonium terephthalate, or tetramethylenediammonium adipate. Alternatively, the polyamide chain can be formedpartially or essentially from ring-opening polymerization of cyclicamides such as caprolactam. The polyamide chain can also be formedpartially or essentially from polymerization of amino acid, includingthose that structurally correspond to the cyclic amides. The polyamidechain can comprise multiple segments formed from the same or differentpolyacids, polyamines, cyclic amides, and/or amino acids, non-limitingexamples of which are disclosed herein. Suitable starting materials alsoinclude polyacid polymers, polyamine telechelics, and amino acidpolymers. At least one polyacid, polyamine, cyclic amide, or amino acidhaving Mw of at least about 200, such as at least about 400, or at leastabout 1,000 can be used to form the backbone. A blend of at least twopolyacids and/or a blend of at least two polyamines can be used, whereinone has a molecular weight greater than the other. The polyacid orpolyamine of smaller molecular weight can contribute to hard segments inthe polyamine polyamide, which may improve shear resistance of theresulting elastomer. For example, the first polyacid/polyamine can havea molecular weight of less than 2,000, and the second polyacid/polyaminecan have a molecular weight of 2,000 or greater. In one example, apolyamine blend can comprise a first polyamine having a Mw of 1,000 orless, such as JEFFAMINE. 400 (Mw of about 400), and a second polyaminehaving a Mw of 1,500 or more, such as JEFFAMINE 2000 (Mw of about2,000). The backbone of the polyamine polyamide can have about 1-100amide linkages, such as about 2-50, or about 2-20. Polyamine polyamidescan be linear, branched, star-shaped, hyper-branched or dendritic (suchas amine-terminated hyper-branched quinoxaline-amide polymers of U.S.Pat. No. 6,642,347, the disclosure of which is incorporated herein byreference).

When the polyurethane prepolymer is reacted with hydroxyl-terminatedcuring agents during the chain-extending step, as described above, theresulting composition is essentially a pure polyurethane composition. Onthe other hand, when the polyurethane prepolymer is reacted with anamine-terminated curing agent during the chain-extending step, anyexcess isocyanate groups in the prepolymer will react with the aminegroups in the curing agent and create urea linkages having the followinggeneral structure:

where x is the chain length, i.e., about 1 or greater, and R and R₁ arestraight chain or branched hydrocarbon chain having about 1 to about 20carbons.

This chain-extending step, which occurs when the polyurethane prepolymeris reacted with hydroxyl-terminated curing agents, amine-terminatedcuring agents, or mixtures thereof, builds-up the molecular weight andextends the chain length of the prepolymer. When the polyurethaneprepolymer is reacted with hydroxyl-terminated curing agents, apolyurethane composition having urethane linkages is produced. When thepolyurethane prepolymer is reacted with amine-terminated curing agents,a polyurethane/urea hybrid composition having urethane and urea linkagesis produced. The polyurethane/urea hybrid composition is distinct fromthe pure polyurethane composition. The concentration of urethane andurea linkages in the hybrid composition may vary. In general, the hybridcomposition may contain a mixture of about 10 to 90 wt. % urethane andabout 90% to 10 wt. % urea linkages. The resulting polyurethanecomposition or polyurethane/urea hybrid composition has elastomericproperties based on phase separation of the soft and hard segments. Thesoft segments, which are formed from the polyol reactants, are generallyflexible and mobile, while the hard segments, which are formed from theisocyanate and chain extenders, are generally stiff and immobile.

The polyurethane compositions used to produce the layer(s) of the golfball of this invention have many advantageous physical properties andfeatures. For example, the flexural modulus (as measured in accordancewith ASTM D-790) of the polyurethane composition is generally about 10to about 150 kpsi, preferably 15 to 125 kpsi, and more preferably 18 to90 kpsi. In addition, the composition has an elongation at break (asmeasured in accordance with ASTM D-638) of about 100 to about 950%,preferably 125 to 750%, and more preferably 200 to 650%; a tensilestrength at break (as measured in accordance with ASTM D-638) of about 1to about 6 kpsi, preferably 2 to 5 kpsi, and more preferably 3 to 4.5kpsi; and a notched Izod strength (as measured in accordance with ASTMD-256) of at least 10, preferably 15 to no break, and more preferably 20to no break as measured at 23° C. The Vicat softening temperature (asmeasured in accordance with ASTM D-1525-70) of the composition ispreferably about 60° to 180° C., and more preferably 75 to 150° C.Lastly, the density (as measured in accordance with ASTM D-792) of thecomposition is about 1.01 to about 1.60, preferably 1.02 to 1.50, andmore preferably 1.03 to 1.30. It is important that the cover material ofthe golf ball has sufficient heat-resistance. If the cover materialsoftens or melts, the dimples on the ball's surface will change shapeand harmfully affect the aerodynamic properties of the ball. Thus, asmentioned above, the Vicat softening temperature of the polyurethanecomposition used to make the cover is preferably about 60° to 180° C.,and more preferably 75 to 150° C.

In addition, the thermoset polyurethane compositions of this inventionhave a cross-link density in the range of about 10 to about 300 mol/m³(moles of effective network chains per cubic meter) and preferably about15 to about 250 mol/m³. The thermoset polyurethanes have good mechanicalstrength and toughness because of their good cross-linking network. Byadjusting the cross-link density of the thermoset polyurethanecomposition, the scuff-resistance, toughness, and durability of theresulting golf ball cover can be improved. It is believed that theincrease in cross-linking density may be due at least in part to theallophanate linkages formed in the reaction of the isocyanate,moisture-resistant polyol, and curing agent. Cross-link density isdefined as moles of effective network chains per cubic meter andcomputed from swelling parameters of the networks and may be measured inaccordance with the procedures described in V. Sekkar, S.Gopalakrishnan, and K. Ambika Devi, Studies on Allophonate-UrethaneNetworks Based on Hydroxyl Terminated Polybutadiene: Effect ofIsocyanate Type on the Network Characteristics, European Polymer Journal39, (2003) (pp. 1281-1290). The test specimens were paced in toluene for48 hrs at ambient conditions. The specimens were removed from thesolvent and weighed after gently wiping off the solvent from the surfaceof the specimen. Subsequently, the solvent absorbed was driven off byplacing the swollen specimen in a vacuum oven at 100° C. for 2 hr andthe weight of the deswollen (dried) specimen was determined From theweights of the swollen and deswollen specimens, and the densities of thepolymer and the solvent, the volume fraction of the polymer in theswollen specimen was calculated. The crosslink densities of the polymernetworks were obtained using Flory-Rhener equation.

Golf Ball Construction

The polyurethane compositions of this invention may be used with anytype of ball construction known in the art. Such golf ball designsinclude, for example, single-piece, two-piece, three-piece, four-piece,and five-piece designs so long as at least one layer comprises apolyurethane composition prepared in accordance with this invention. Thecore, intermediate, and/or cover portions of the ball may be single ormulti-layered.

Core

The cores in the golf balls of this invention may be solid, semi-solid,hollow, fluid-filled, or powder-filled. Typically, the cores are solidand made from rubber compositions containing a base rubber, free-radicalinitiator agent, cross-linking co-agent, and fillers. The base rubbermay be selected, for example, from polybutadiene rubber, polyisoprenerubber, natural rubber, ethylene-propylene rubber, ethylene-propylenediene rubber, styrene-butadiene rubber, and combinations of two or morethereof. A preferred base rubber is polybutadiene. Another preferredbase rubber is polybutadiene optionally mixed with one or moreelastomers such as polyisoprene rubber, natural rubber, ethylenepropylene rubber, ethylene propylene diene rubber, styrene-butadienerubber, polystyrene elastomers, polyethylene elastomers, polyurethaneelastomers, polyurea elastomers, acrylate rubbers, polyoctenamers,metallocene-catalyzed elastomers, and plastomers. As discussed furtherbelow, highly neutralized acid copolymers (HNPs), as known in the art,also can be used to form the core layer.

The base rubber typically is mixed with at least one reactivecross-linking co-agent to enhance the hardness of the rubbercomposition. Suitable co-agents include, but are not limited to,unsaturated carboxylic acids and unsaturated vinyl compounds. Apreferred unsaturated vinyl is trimethylolpropane trimethacrylate. Therubber composition is cured using a conventional curing process.Suitable curing processes include, for example, peroxide curing, sulfurcuring, high-energy radiation, and combinations thereof. In oneembodiment, the base rubber is peroxide cured. Organic peroxidessuitable as free-radical initiators include, for example, dicumylperoxide; n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. Cross-linkingagents are used to cross-link at least a portion of the polymer chainsin the composition. Suitable cross-linking agents include, for example,metal salts of unsaturated carboxylic acids having from 3 to 8 carbonatoms; unsaturated vinyl compounds and polyfunctional monomers (forexample, trimethylolpropane trimethacrylate); phenylene bismaleimide;and combinations thereof. In a particular embodiment, the cross-linkingagent is selected from zinc salts of acrylates, diacrylates,methacrylates, and dimethacrylates. In another particular embodiment,the cross-linking agent is zinc diacrylate (“ZDA”). Commerciallyavailable zinc diacrylates include those selected from RocklandReact-Rite and Sartomer.

The rubber compositions also may contain “soft and fast” agents such asa halogenated organosulfur, organic disulfide, or inorganic disulfidecompounds. Particularly suitable halogenated organosulfur compoundsinclude, but are not limited to, halogenated thiophenols. Preferredorganic sulfur compounds include, but not limited to,pentachlorothiophenol (“PCTP”) and a salt of PCTP. A preferred salt ofPCTP is ZnPCTP. A suitable PCTP is sold by the Struktol Company (Stow,Ohio) under the tradename, A95 ZnPCTP is commercially available fromEchinaChem (San Francisco, Calif.). These compounds also may function ascis-to-trans catalysts to convert some cis-1,4 bonds in thepolybutadiene to trans-1,4 bonds. Antioxidants also may be added to therubber compositions to prevent the breakdown of the elastomers. Otheringredients such as accelerators (for example, tetra methylthiuram),processing aids, dyes and pigments, wetting agents, surfactants,plasticizers, as well as other additives known in the art may be addedto the rubber composition. The core may be formed by mixing and formingthe rubber composition using conventional techniques. These cores can beused to make finished golf balls by surrounding the core with outer corelayer(s), intermediate layer(s), and/or cover materials as discussedfurther below. In another embodiment, the cores can be formed usinghighly neutralized polymer (HNP) compositions as disclosed in U.S. Pat.Nos. 6,756,436, 7,030,192, 7,402,629, and 7,517,289. The cores from thehighly neturalized polymer compositions can be further cross-linkedusing any free-radical initiation sources including radiation sourcessuch as gamma or electron beam as well as chemical sources such asperoxides and the like. The core may contain sections having the samehardness or different hardness levels. That is, there can be uniformhardness throughout the different sections of the core or there can behardness gradients across the layers. For example, in single cores,there may be a hard-to-soft gradient (a “positive” gradient) from thesurface of the core to the geometric center of the core. In otherinstances, the there may be a soft-to-hard gradient (a “negative”gradient) or zero hardness gradient from the core's surface to thecore's center. For dual core golf balls, the inner core layer may have asurface hardness that is less than the geometric center hardness todefine a first “negative” gradient. As discussed above, an outer corelayer may be formed around the inner core layer, and the outer corelayer may have an outer surface hardness less than its inner surfacehardness to define a second “negative” gradient. In other versions, thehardness gradients from surface to center may be hard-to-soft(“positive”), or soft-to-hard (“negative”), or a combination of bothgradients. In still other versions the hardness gradients from surfaceto center may be “zero” (that is, the hardness values are substantiallythe same.) Methods for making cores having positive, negative, and zerohardness gradients are known in the art as described in, for example,U.S. Pat. Nos. 7,537,530; 7,537,529; 7,427,242; and 7,410,429, thedisclosures of which are hereby incorporated by reference.

Golf balls made in accordance with this invention can be of any size,although the USGA requires that golf balls used in competition have adiameter of at least 1.68 inches and a weight of no greater than 1.62ounces. For play outside of USGA competition, the golf balls can havesmaller diameters and be heavier. For example, the diameter of the golfball may be in the range of about 1.68 to about 1.80 inches. In FIG. 1,one version of a golf ball that can be made in accordance with thisinvention is generally indicated at (10). Various patterns and geometricshapes of dimples (11) can be used to modify the aerodynamic propertiesof the golf ball (10). The dimples (11) can be arranged on the surfaceof the ball (10) using any suitable method known in the art. In oneembodiment, as shown in FIG. 2, the core is a single-piece having anoutside diameter of about 1.00 to about 1.65 inches. Preferably, thesingle-piece core has a diameter of about 1.50 to about 1.64 inches. Thecore generally makes up a substantial portion of the ball, for example,the core may constitute at least about 90% of the ball. The hardness ofthe core may vary depending upon desired properties of the ball. Ingeneral, core hardness is in the range of about 50 to about 90 Shore Cand more preferably in the range of about 55 to about 75 Shore C. Thecompression of the core is generally in the range of about 30 to about110 and more preferably in the range of about 50 to about 100. In asecond embodiment, as shown in FIG. 3, the core is made up of twopieces. The inner core (22) may be made of a rubber or other suitablecomposition as described above, while the outer core layer (24) may bemade of the polyurethane composition of this invention. In a preferredversion, the outer core layer has a thickness in the range of about0.030 to about 0.070 inches and a Shore D surface hardness in the rangeof about 50 to about 90 and more preferably in the range of about 55 toabout 75 Shore D.

Intermediate and Cover Layers

The golf balls of this invention preferably include at least oneintermediate layer. As used herein, the term, “intermediate layer” meansa layer of the ball disposed between the core and cover. Theintermediate layer may be considered an outer core layer or inner coverlayer or any other layer disposed between the inner core and outer coverof the ball. The intermediate layer also may be referred to as a casingor mantle layer. The intermediate layer preferably has water vaporbarrier properties to prevent moisture from penetrating into the rubbercore. The ball may include one or more intermediate layers disposedbetween the inner core and outer cover.

The polyurethane composition of this invention can be used to make theouter core, intermediate layer, inner cover, and/or outer cover. In someinstances, a traditional thermoplastic or thermosetting composition maybe used to make one layer, and the polyurethane composition may be usedto make a different layer of the golf ball depending upon the desiredball construction playing performance properties. If a conventionalthermoplastic or thermosetting composition is used in one layer (and thepolyurethane composition used in a different layer), then a wide varietyof thermoplastic or thermosetting materials can be employed. Thesematerials include for example, olefin-based copolymer ionomer resins(for example, Surlyn® ionomer resins and DuPont HPF® 1000 and HPF® 2000,commercially available from E. I. du Pont de Nemours and Company; Iotek®ionomers, commercially available from ExxonMobil Chemical Company;Amplify® IO ionomers of ethylene acrylic acid copolymers, commerciallyavailable from The Dow Chemical Company; and Clarix® ionomer resins,commercially available from A. Schulman Inc.); polyurethanes; polyureas;copolymers and hybrids of polyurethane and polyurea; polyethylene,including, for example, low density polyethylene, linear low densitypolyethylene, and high density polyethylene; polypropylene;rubber-toughened olefin polymers; acid copolymers, for example,poly(meth)acrylic acid, which do not become part of an ionomericcopolymer; plastomers; flexomers; styrene/butadiene/styrene blockcopolymers; styrene/ethylene-butylene/styrene block copolymers;dynamically vulcanized elastomers; copolymers of ethylene and vinylacetates; copolymers of ethylene and methyl acrylates; polyvinylchloride resins; polyamides, poly(amide-ester) elastomers, and graftcopolymers of ionomer and polyamide including, for example, Pebax®thermoplastic polyether block amides, commercially available from ArkemaInc; cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromE. I. du Pont de Nemours and Company; polyurethane-based thermoplasticelastomers, such as Elastollan®, commercially available from BASF;synthetic or natural vulcanized rubber; and combinations thereof.

The polyurethane composition constituting the layer(s) of the golf ballmay contain additives, ingredients, and other materials in amounts thatdo not detract from the properties of the final composition. Theseadditive materials include, but are not limited to, activators such ascalcium or magnesium oxide; fatty acids such as stearic acid and saltsthereof; fillers and reinforcing agents such as organic or inorganicparticles, for example, clays, talc, calcium, magnesium carbonate,silica, aluminum silicates zeolites, powdered metals, and organic orinorganic fibers, plasticizers such as dialkyl esters of dicarboxylicacids; surfactants; softeners; tackifiers; waxes; ultraviolet (UV) lightabsorbers and stabilizers; antioxidants; optical brighteners; whiteningagents such as titanium dioxide and zinc oxide; dyes and pigments;processing aids; release agents; and wetting agents.

The polyurethanes of this invention may be blended with non-ionomericand olefin-based ionomeric polymers to form the composition that will beused to make the golf ball layer. Examples of non-ionomeric polymersinclude vinyl resins, polyolefins including those produced using asingle-site catalyst or a metallocene catalyst, polyurethanes,polyureas, polyamides, polyphenylenes, polycarbonates, polyesters,polyacrylates, engineering thermoplastics, and the like. The blend maycontain about 10 to about 90% by weight of the polyurethane and about 90to about 10% by weight of a non-ionomeric polymer. Particularly, theblend may contain a lower concentration of polyurethane in the amount of10%, 20%, 30%, 40%, or 50% and an upper concentration of polyurethane inthe amount of 60%, 70%, 80%, or 90%. Conversely, the concentration ofnon-ionomeric polymer may be relatively high (60%, 70%, 80%, or 90%) orrelatively low (10%, 20%, 30%, 40%, or 50%.)

Olefin-based ionomers, such as ethylene-based copolymers, normallyinclude an unsaturated carboxylic acid, such as methacrylic acid,acrylic acid, or maleic acid. Other possible carboxylic acid groupsinclude, for example, crotonic, maleic, fumaric, and itaconic acid. “Lowacid” and “high acid” olefin-based ionomers, as well as blends of suchionomers, may be used. In general, low acid ionomers are considered tobe those containing 16 wt. % or less of carboxylic acid, whereas highacid ionomers are considered to be those containing greater than 16 wt.% of carboxylic acid. The acidic group in the olefin-based ioniccopolymer is partially or totally neutralized with metal ions such aszinc, sodium, lithium, magnesium, potassium, calcium, manganese, nickel,chromium, copper, or a combination thereof. For example, ionomericresins having carboxylic acid groups that are neutralized from about 10percent to about 100 percent may be used. In one embodiment, the acidgroups are partially neutralized. That is, the neutralization level isfrom 10 to 80%, more preferably 20 to 70%, and most preferably 30 to50%. In another embodiment, the acid groups are highly or fullyneutralized. That is, the neutralization level is from 80 to 100%, morepreferably 90 to 100%, and most preferably 95 to 100%. The blend maycontain about 10 to about 90% by weight of the polyurethane and about 90to about 10% by weight of a partially, highly, or fully-neutralizedolefin-based ionomeric copolymer. Particularly, the blend may contain alower concentration of polyurethane in the amount of 10%, 20%, 30%, 40%,or 50% and an upper concentration of polyurethane in the amount of 60%,70%, 80%, or 90%. Conversely, the concentration of non-ionomeric polymermay be relatively high (60%, 70%, 80%, or 90%) or relatively low (10%,20%, 30%, 40%, or 50%). The above-mentioned blends may contain one ormore suitable compatibilizers such as glycidyl acrylate or glycidylmethacrylate or maleic anhydride containing-polymers.

Golf Ball Dimensions and Properties

As discussed above, the polyurethane compositions of this invention maybe used with any type of ball construction known in the art. Such golfball designs include, for example, two-piece, three-piece, four-piece,and five-piece designs with single or multi-layered cores, intermediateand cover portions. The thickness and diameter of the different layersalong with properties such as hardness and compression may varydepending upon the desired playing performance properties of the golfball such as initial velocity, spin control, and feel.

Referring to FIG. 2, a three-piece golf ball (12) that can be made inaccordance with this invention is illustrated. In this version, the ball(12) includes a solid core (14), an intermediate casing layer (16) andcover layer (18) made of the polyurethane composition, The core (14) ismade of polybutadiene rubber or other suitable material as describedabove and preferably has a diameter in the range of about 1.30 to about1.60 inches. The intermediate layer (16) is made of a thermoplastic orthermoset composition as described above. For example, the intermediatelayer (16) may be formed from a compound selected from the groupconsisting of olefin-based ionomer copolymers; polyesters;polyester-ether elastomers; polyester-ester elastomers; polyamides;polyamide-ether elastomers, and polyamide-ester elastomers;polyurethanes, polyureas, and polyurethane-polyurea hybrids; andmixtures thereof. The range of thickness for the intermediate layer (16)may vary, but it generally has a thickness of about 0.015 to about 0.070inches, preferably about 0.020 to about 0.050 inches, and morepreferably about 0.025 to about 0.040 inches. The intermediate layer(16) preferably has a Shore D surface hardness of 45 to 75, preferably55 to 70, and most preferably 60 to 65. The thickness of the cover layer(18) may vary, but it is generally in the range of about 0.015 to about0.090 inches and more preferably 0.020 to about 0.040 inches.

In one preferred version of a three-piece golf ball, the core has afirst Shore C surface hardness of C₁ in the range of about 50 to 90 andthe cover layer has a second Shore D surface hardness of C₂ in the rangeof about 60 to 95. The ratio of C₂ to C₁ is in the range of about 0.6 to1.4. It should be understood the three-piece golf ball constructionshown in FIG. 2 is for illustrative purposes only and not meant to berestrictive. Other three-piece constructions can be made per thisinvention. For example, the intermediate layer (16) may be made of thepolyurethane composition of this invention and the cover layer (18) maybe made of a conventional thermoset or thermoplastic composition. Inanother embodiment, the intermediate and cover layers each may be formedfrom the polyurethane resin of this invention. Different additives maybe incorporated into the resins, and the layers may have similar ordifferent hardness levels. In order to make a visible distinctionbetween the layers, various colorants, dyes, pigments, and the like canbe added to the respective resins.

In FIG. 3, a four-piece golf ball (20) having a multi-layered core isillustrated. The multi-layered core includes an inner core (22) andouter core layer (24). The inner core (22) may be made of a first rubbermaterial, for example, polybutadiene, or highly neutralized polymer(HNP) and the outer core layer (24) may be made of the polyurethanecomposition of this invention. The golf ball further includes anintermediate casing layer (26) and cover layer (28), which may have thesame thickness dimensions as described above. Conventional thermoplasticor thermoset resins such as olefin-based ionomeric copolymers,polyamides, polyesters, polycarbonates, polyolefins, polyurethanes, andpolyureas as described above can be used to make the casing layer (26)and/or cover layer (28). In such multi-layered cores, the inner core(22) preferably has a diameter of about 0.50 to about 1.30 inches, morepreferably 1.00 to 1.15 inches, and may be relatively soft (that is, itmay have a compression of less than about 30.) Meanwhile, theencapsulating outer core layer (24) generally has a thickness of about0.030 to about 0.070 inches, preferably 0.035 to 0.065 inches and may berelatively hard (compression of about 70 or greater.) That is, thetwo-piece core, which is made up of the inner core (22) and outer corelayer (24), preferably has a total diameter of about 1.50 to about 1.64inches, more preferably 1.510 to 1.620 inches, and a compression ofabout 80 to about 115, more preferably 85 to 110.

In FIG. 3, the illustrated four-piece golf ball is not meant to belimiting. Other four-piece constructions can be made per this invention.For example, the intermediate casing layer (26) and/or cover layer (28)may be made of the same polyurethane composition of this invention.Different additives may be incorporated into the resins, and the layersmay have similar or different hardness levels. In order to make avisible distinction between the layers, various colorants, dyes,pigments, and the like can be added to the respective resins.

Turning to FIG. 4, a four-piece golf ball (30) having a multi-layeredcover is shown. The ball (30) includes a solid, rubber center (33), anouter core layer (34), and multi-layered cover constituting an innercover layer (31) and outer cover layer (32). The solid rubber center(33) preferably has a diameter of about 0.50 to about 1.30 inches, andmore preferably 1.00 to 1.15 inches, while the surrounding outer corelayer (34) preferably has a thickness of about 0.030 to about 0.070inches, and more preferably 0.035 to 0.065 inches. In this version, theinner cover layer (31) is made of a conventional thermoplastic orthermosetting resin and the outer cover layer (32) is made of thepolyurethane composition of this invention. The inner cover layer (31)preferably has a thickness of about 0.020 to about 0.050 inches andShore C surface hardness of about 60 to about 95. The inner cover (31)may be made of an ionomer resin or any other suitable inner covermaterial as described above. The outer cover layer (32), which surroundsthe inner cover layer (31), is preferably made of the polyurethanecomposition of this invention. The outer cover layer (32) preferably hasa thickness in the range of about 0.020 to about 0.035 inches and aShore C surface hardness in the range of about 50 to about 90. Thefour-piece golf ball construction shown in FIG. 4 is but one example andother four-piece constructions can be made in accordance with thisinvention. For instance, in another version, the inner cover layer (31)may be made of the polyurethane composition of this invention. The innerand outer cover layers may be of different hardness levels. In onepreferred embodiment, the inner cover has a greater hardness than theouter cover.

In FIG. 5, a five-piece golf ball (40) having a cover with three-layersis shown. The ball includes a solid, rubber center (41), an outer corelayer (44), and multi-layered cover constituting an inner cover layer(46), intermediate cover layer (48) and outer cover layer (50). In thisversion, the inner and intermediate cover layers (46, 48) are made ofconventional thermoplastic or thermosetting resins and the outer coverlayer (50) is made of the polyurethane composition of this invention.The inner cover layer (46) preferably has a Shore C surface hardness ofabout 60 to about 95. The intermediate cover (48) preferably has a ShoreC surface hardness of about 30 to about 50. The outer cover layer (50)preferably has a Shore C surface hardness of about 60 to about 95. Thatis, in one preferred embodiment, the intermediate cover layer (48) has aShore C surface hardness that is softer than both the inner cover layer(46) and outer cover layer (50).

As noted above, the golf ball constructions shown in FIGS. 1-5 are forillustrative purposes only and are not meant to be restrictive. A widevariety of golf ball constructions may be made in accordance with thepresent invention depending upon the desired properties of the ball solong as at least one layer contains the polyurethane composition of thisinvention.

Preferably, the overall diameter of the core and all intermediate layersis about 80 percent to about 98 percent of the overall diameter of thefinished ball. The core may have a diameter ranging from about 0.50inches to about 1.65 inches. In one embodiment, the diameter of the coreis about 1.20 inches to about 1.63 inches. For example, if a two-pieceball having a core and polyurethane cover of this invention is made, thecore may have a diameter ranging from about 1.50 inches to about 1.62inches. The core may further include a moisture-resistant surface toprevent moisture from penetrating there in. When the core includes aninner core layer (center) and an outer core layer, the inner core layeris preferably about 0.50 inches or greater and the outer core layerpreferably has a thickness of about 0.10 inches or greater. For example,when a multi-layer core is made, the center may have a diameter rangingfrom about 0.5 inches to about 1.30 inches and the outer core layer mayhave a diameter ranging from about 0.12 inches to about 0.5 inches. Thepolyurethane cover of this invention has a thickness to providesufficient strength, good performance characteristics, and durability.In one embodiment, the cover thickness is from about 0.150 inches toabout 0.090 inches, preferably about 0.070 inches or less. For example,when a two-piece ball according to invention is made, the cover may havea thickness ranging from about 0.030 inches to about 0.090 inches. Inanother instance, when a three-piece ball is made, the thickness of thecover may be about 0.020 to 0.060 inches. Likewise, the range ofthicknesses for the intermediate layer may vary, because theintermediate layer may be used in many different constructions and morethan one intermediate layer may be included in the ball. For example,the intermediate layer may be used as an outer core layer, an innercover layer, and/or a moisture/vapor barrier layer. In general, theintermediate layer may have a thickness of about 0.120 inches or less.In general, the thickness of the intermediate layer is about 0.015 toabout 0.120 inches and preferably about 0.020 to about 0.060 inches. Inone embodiment, the thickness of the intermediate layer is from about0.015 inches to about 0.100 inches.

The hardness of the golf ball (or subassembly such as the core) may varydepending upon the ball construction and desired performance properties.The test methods for measuring surface and material hardness aredescribed in further detail below. In general, surface or materialhardness refers to the firmness of the surface or material. The relativehardness levels of the core layer, intermediate layer(s), and coverlayer are primary factors in determining distance performance and spinrate of the ball. As a general rule, when the ball has a relatively softcover, the initial spin rate of the ball is relatively high and when theball has a relatively hard cover, the initial spin rate of the ball isrelatively low. Furthermore, in general, when the ball contains arelatively soft core, the resulting spin rate of the ball is relativelylow. The compressive force acting on the ball is less when the cover iscompressed by the club face against a relatively soft core. The clubface is not able to fully interface with the ball and thus the initialspin rate on the ball is lower. On the other hand, when the ballcontains a relatively hard core, the resulting spin rate of the ball isrelatively high. The club face is able to more fully interface with theball and thus the initial spin rate of the ball. The surface hardness ofa golf ball layer (or other spherical surface) is obtained from theaverage of a number of measurements taken from opposing hemispheres,taking care to avoid making measurements on the parting line of the coreor on surface defects such as holes or protrusions. In general, the CORof the ball will increase as the hardness of the ball is increased. Thetest methods for measuring surface and material hardness are describedin further detail below.

As discussed above, in one version of the golf ball of the presentinvention, the core preferably has a first surface hardness (C₁) in therange of about 50 to about 95 Shore C, more preferably about 55 to about85 Shore C, and most preferably about 60 to about 75 Shore C. Meanwhile,the cover layer preferably has a second surface hardness (C₂) in therange of about 65 to about 95 Shore C, more preferably about 65 to about90 Shore C, and most preferably about 70 to about 85 Shore C. And, theratio of C₂ to C₁ is in the range of 0.6 to 1.4.

In yet another embodiment, the hardness of the core (C₁) is in the rangeof about is about 55 to about 95 Shore C and more preferably about 60 toabout 90 Shore C. Meanwhile, the cover layer preferably has a secondsurface hardness (C₂) in the range of about 50 to about 95 Shore C andmore preferably about 60 to about 85 Shore C. And, the ratio of C₂ to C₁is in the range of 0.5 to 1.5.

The intermediate layer(s) may also vary in hardness. In one embodiment,the hardness of the intermediate layer is in the range of about 30 toabout 90 Shore D, preferably about 80 Shore D or less, and morepreferably about 70 Shore D or less. For example, when an intermediatelayer is formed from the composition of the invention, the hardness ofthe intermediate layer may be about 65 Shore D or less, preferablyranging from about 35 to about 60 Shore D. In yet another embodiment,the hardness of the intermediate layer is about 50 Shore D or greater,preferably about 55 Shore D or greater. In one embodiment, theintermediate layer hardness is from about 55 to about 65 Shore D.

There are several other physical properties of the golf ball that affectthe ball's playing performance For example, the compression of the corecan affect the ball's spin rate off the driver as well as the “feel” ofthe ball as the club face makes impact with the ball. In general, ballswith relatively low compression values have a softer feel. As disclosedin Jeff Dalton's Compression by Any Other Name, Science and Golf IV,Proceedings of the World Scientific Congress of Golf (Eric Thain ed.,Routledge, 2002) (“J. Dalton”) several different methods can be used tomeasure compression including Atti compression, Riehle compression,load/deflection measurements at a variety of fixed loads and offsets,and effective modulus. The test methods for measuring compression inaccordance with the present invention are described in further detailbelow.

The “coefficient of restitution” or “COR” of a golf ball is also anotherimportant property and this refers to the ratio of a ball's reboundvelocity to its initial incoming velocity when the ball is fired out ofan air cannon into a rigid vertical plate. The COR for a golf ball iswritten as a decimal value between zero and one. A golf ball may havedifferent COR values at different initial velocities. The United StatesGolf Association (USGA) sets limits on the initial velocity of the ballso one objective of golf ball manufacturers is to maximize the COR underthese conditions. Balls with a higher rebound velocity have a higher CORvalue. Such golf balls rebound faster, retain more total energy whenstruck with a club, and have longer flight distance. In general, the CORof the ball will increase as the hardness of the ball is increased. Thetest methods for measuring COR are described in further detail below.

The golf balls of the present invention preferably have a “coefficientof restitution” (“COR”) of at least 0.750 and more preferably at least0.800 and compression of from about 70 to about 110, preferably from 90to 100.

The moisture vapor transmission rate (MVTR) of the layers in the golfball also is significant in golf ball design and construction. Asdiscussed above, the inner core (or center) helps provide resiliency tothe golf ball. As the core absorbs water, it tends to lose itsresiliency. The compression and COR of the ball may be reducedsignificantly if a large amount of water vapor permeates into the core.Layers of the golf balls, which are made of the polyurethane compositionof this invention, help minimize moisture penetration into the core.Preferably, the moisture vapor barrier layer has a thickness of 0.002 to0.010 inches, and a moisture vapor transmission rate of less than about4.0 grams·mm/m²·day, more preferably less than 3 grams·mm/m²·day, andmost preferably less than 1.0 grams·mm/m²·day, particularly 0.5 to 1.0grams·mm/m²·day. The moisture vapor transmission rate is defined as themass of moisture vapor that diffuses into a material of a giventhickness per unit area per unit time. The test methods for measuringMVTR are described in further detail below.

Methods of Constructing Golf Ball Layers

The golf balls of the invention may be formed using a variety ofapplication techniques such as compression molding, flip molding,injection molding, retractable pin injection molding, reaction injectionmolding (RIM), liquid injection molding (LIM), casting, vacuum forming,powder coating, flow coating, spin coating, dipping, spraying, and thelike. Conventionally, compression molding and injection molding areapplied to thermoplastic materials, whereas RIM, liquid injectionmolding, and casting are employed on thermoset materials. These andother manufacturing methods are disclosed in U.S. Pat. Nos. 6,207,784and 5,484,870, the disclosures of which are hereby incorporated byreference. The cores of the golf balls of the invention may be formed byany suitable method known to those of ordinary skill in art. When thecores are formed from a thermoset material, compression molding is aparticularly suitable method of forming the core. On the other hand, thecores may be injection molded when the cores are formed using athermoplastic material.

More particularly, the polyurethane composition of this invention usedto form the thermoset cover of other layer of the golf ball of thisinvention is a castable, reactive liquid that can be applied over thegolf ball subassembly (for example, core and overlying casing layer)using any suitable application technique spraying, dipping, spincoating, or flow coating methods which are known in the art. The liquidnature of the polyurethane composition of this invention makes itpossible to be applied as a thin outer cover layer to the golf ball. Forexample, in one version of the casting method, the polyurethane mixtureis dispensed into the cavity of an upper mold member. This firstmold-half has a hemispherical structure. Then, the cavity of acorresponding lower mold member is filled with the polyurethane mixture.This second mold-half also has a hemispherical structure. The cavitiesare typically heated beforehand. A ball cup holds the golf ballsubassembly (core and overlying casing layer) under vacuum. After thepolyurethane mixture in the first mold-half has reached a semi-gelled orgelled sate, the pressure is removed and the golf ball is lowered intothe upper mold-half containing the polyurethane mixture. Then, the firstmold-half is inverted and mated with the second mold-half containingpolyurethane mixture which also has reached a semi-gelled or gelledstate. The polyurethane mixtures, contained in the mold members that aremated together, form the golf ball cover. The mated first and secondmold-halves containing the polyurethane mixture and golf ball center maybe next heated so that the mixture cures and hardens. Then, the golfball is removed from the mold and heated and cooled accordingly.

The intermediate layer and/or cover layer may also be formed using anysuitable method known to those of ordinary skill in the art. Forexample, an intermediate layer may be formed by blow molding orretractable pin molding and covered with a dimpled cover layer formed byinjection molding, compression molding, casting, vacuum forming, powdercoating, and the like. The use of various dimple patterns and profilesprovides a relatively effective way to modify the aerodynamiccharacteristics of a golf ball. As such, the manner in which the dimplesare arranged on the surface of the ball can be by any available method.For instance, the ball may have an icosahedron-based pattern, such asdescribed in U.S. Pat. No. 4,560,168, or an octahedral-based dimplepatterns as described in U.S. Pat. No. 4,960,281. Furthermore, theresultant golf balls prepared according to the invention typically willhave dimple coverage greater than about 60 percent, preferably greaterthan about 65 percent, and more preferably greater than about 70percent.

Golf Ball Post-Cross-Linking

The components in the golf balls of this invention may be cross-linkedby a variety of chemical and irradiation methods. For example, peroxidesor sulfur-based agents can be used to induce cross-linking of thepolymer chains. High-energy radiation, which is capable of generatingfree radicals, also may be used to cross-link the composition.Preferably, the polyurethane compositions of this invention demonstratean increase in Shore D surface hardness of at least 2.5% upon beingtreated with chemical and/or irradiation methods to inducecross-linking. More preferably, the increase in Shore D surface hardnessis in the range of about 2.5 to 20%. Ordinarily, the thermosetpolyurethane compositions of this invention have a relatively highamount of cross-linking in their polymer chains. When these thermosetpolyurethane compositions, along with the other components in the golfball, undergo a post cross-linking process, there should be additionalcross-linking. The resulting golf ball will have increased hardness andtoughness, but there will be no substantial loss in physical propertiessuch as cut/tear-resistance; scuff/wear-resistance; or playingperformance such as the soft feel and shot control of the ball. That is,even though the post cross-linking process generates a ball havinghigher hardness, the cover of the ball does not become brittle and thereis no sacrifice of other physical properties. The ball covers maintaintheir high durability and resiliency as well as soft feel. It isbelieved that this increase in hardness while maintaining the otherdesirable properties is due to the building blocks used to make thethermoset polyurethane composition, particularly the polyisocyanates,moisture-resistant polyols, and curing agents of this invention.

Examples of suitable radiation sources include electron beams,ultra-violet (UV), gamma, X-ray, and infrared rays, heat, andcombinations thereof. Organic peroxides that can be used as free-radicalinitiators include, for example, dicumyl peroxide;n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. The peroxidefree-radical initiators are generally present in the polyurethanecomposition in an amount within the range of 0.05 to 15 parts by weightper 100 parts of the base composition.

Cross-linking agents having an average functionality greater than 2.0can be added to the composition. For example, the cross-linking agentcan be added to the mixture of the isocyanate compound,moisture-resistant polyol, and chain extender. Suitable cross-linkingagents include, for example, metal salts of unsaturated carboxylic acidshaving from 3 to 8 carbon atoms; unsaturated vinyl compounds andpolyfunctional monomers (for example, trimethylolpropane trimethacrylate(TMP and pentaerythritol)); phenylene bismaleimide; and combinationsthereof. Particularly suitable metal salts include, for example, one ormore metal salts of acrylates, diacrylates, methacrylates, anddimethacrylates, wherein the metal is selected from magnesium, calcium,zinc, aluminum, lithium, and nickel. In a particular embodiment, thecross-linking agent is selected from zinc salts of acrylates,diacrylates (ZDA), methacrylates, and dimethacrylates. The cross-linkingagent typically is included in the base composition in an amount withinthe range of 1 to 70 parts.

The composition may further contain one or more photoinitiators that canbe activated by actinic radiation and initiate free radicalcross-linking. Suitable photoinitiators include, for example, aromaticketone compounds such as benzophenones, in combination with tertiaryamines, alkylbenzophenones, 4,4′-bis(dimethylamino)benzophenone(Michler's ketone), anthrone and halogenated benzophenones or mixturesof said types. Other photoinitiators, such as benzoin and itsderivatives, benzyl ketals, acylphosphine oxides, for example,2,4,6-tri-methylbenzoyldiphenylphosphine oxide, bisacylophosphineoxides, phenylglyoxylic acid esters, camphorquinone,.α-aminoalkylphenones, .α,α-dialkoxyacetophenones,1-[4-(phenylthio)phenyl]octane-1,2-dione-2-(O-benzoyloxime) andα-hydroxyalkylphenones, are suitable. The photoinitiator typically isincluded in the base composition in aan amount within the range of 0.1to 10 weight percent.

As noted above, high energy radiation may be used to inducecross-linking. Gamma radiation penetrates relatively deep into thematerial undergoing irradiation, but also increases cross-linking of theinner core. Accordingly, the compression of the core can be adjusted toallow for any increase in hardness that results from the cross-linking.The type of radiation source used will depend in part upon thecomposition of the underlying layers in the golf ball. In addition, thelevel of irradiation will depend upon the desired end properties andcharacteristics of the finished golf ball.

The golf balls of this invention may be post-processed usingconventional techniques as is customary in the industry. For example,the golf ball cover may first be painted with a composition comprisingwhite or other colored concentrate. Then, indicia (such as a ballnumber, a ball brand name, and/or a company name or logo) can be appliedto the surface of the ball using a pad-printing process. Once the inkindicia have been printed on the ball, a clear protective top-coat iscommonly applied over the print to provide the ball with a shinysurface. The top-coat provides the ball with a smooth, substantiallytack-free surface. A prime coat, typically a film about one-half thethickness of the clear coat, may be applied before production printingor over the production print and before application of the clear coat.

Because the polyurethane compositions of the invention may be used inany layer of a golf ball, the golf ball construction, physicalproperties, and resulting performance may vary greatly depending on thelayer(s) of the ball that include the compositions of this invention.The polyurethane compositions provide the golf ball with advantageousproperties and features. For example, as discussed above, thecompositions may be used to make the outer core, intermediate layer,inner cover, and/ore outer cover. As discussed above, the molecularweight of the thermoset polyurethane composition may increase and thehardness of the ball may increase due to the post cross-linkingmechanism, but the resulting ball does not exhibit brittleness or otherundesirable physical properties. Of course, the cross-linking density ofthe thermoset polyurethane composition also increases during this postcross-linking treatment. That is, the cross-link density of thepolyurethane composition that has been further cross-linked by chemicalor radiation treatment is greater than the cross-link density of thestarting polyurethane composition. The cover of the ball retains itshigh impact durability and cut/tear-resistance. The ball has highresiliency so that it shows good flight distance when hit off a tee. Atthe same time, the ball maintains a soft “feel” so that its flight pathcan be controlled on approach shots near the green. The combination ofthe core and cover layer(s) made from the polyurethane composition ofthis invention results in a golf ball having enhanced resiliency anddurability characteristics while maintaining the desirable feel andplayability of the ball. The polyurethane composition can be used tomanufacture golf balls having an optimum combination of high resiliency,impact durability, and soft feel. The combination of the polyurethaneand other materials comprising the core, intermediate layer and/or coverlayer provides a finished ball that can be used to achieve increaseddistance. And yet, the golf ball retains a relatively soft feel and hasa good spin rate Thus, players can more easily control the play of theball.

Test Methods

Hardness Shore D Hardness measurements are made pursuant to ASTM D-2240“Indentation Hardness of Rubber and Plastic by Means of a Durometer.”Because of the curved surface of the golf ball layer, care must be takento ensure that the golf ball or golf ball subassembly is centered underthe durometer indentor before a surface hardness reading is obtained. Acalibrated digital durometer, capable of reading to 0.1 hardness units,is used for all hardness measurements and is set to take hardnessreadings at 1 second after the maximum reading is obtained. The digitaldurometer must be attached to and its foot made parallel to the base ofan automatic stand. The weight on the durometer and attack rate conformsto ASTM D-2240. It should be understood that there is a fundamentaldifference between “material hardness” and “hardness as measureddirectly on a golf ball.” For purposes of the present invention,material hardness is measured according to ASTM D2240 and generallyinvolves measuring the hardness of a flat “slab” or “button” formed ofthe material. Surface hardness as measured directly on a golf ball (orother spherical surface) typically results in a different hardnessvalue. The difference in “surface hardness” and “material hardness”values is due to several factors including, but not limited to, ballconstruction (that is, core type, number of cores and/or cover layers,and the like); ball (or sphere) diameter; and the material compositionof adjacent layers. It also should be understood that the twomeasurement techniques are not linearly related and, therefore, onehardness value cannot easily be correlated to the other. JIS-C hardnesswas measured according to the test methods JIS K 6301-1975. Shore Chardness was measured according to the test methods D2240-05.

Compression For purposes of the present invention, “compression” refersto Atti compression and is measured according to a known procedure,using an Atti compression device, wherein a piston is used to compress aball against a spring. The travel of the piston is fixed and thedeflection of the spring is measured. The measurement of the deflectionof the spring does not begin with its contact with the ball; rather,there is an offset of approximately the first 1.25 mm (0.05 inches) ofthe spring's deflection. Cores having a very low stiffness will notcause the spring to deflect by more than 1.25 mm and therefore have azero compression measurement. The Atti compression tester is designed tomeasure objects having a diameter of 1.680 inches; thus, smallerobjects, such as golf ball cores, must be shimmed to a total height of1.680 inches to obtain an accurate reading. Conversion from Atticompression to Riehle (cores), Riehle (balls), 100 kg deflection, 130-10kg deflection or effective modulus can be carried out according to theformulas given in J. Dalton.

Coefficient of Restitution (“COR”) In the present invention, COR isdetermined according to a known procedure, wherein a golf ball or golfball subassembly (for example, a golf ball core) is fired from an aircannon at two given velocities and a velocity of 125 ft/s is used forthe calculations. Ballistic light screens are located between the aircannon and steel plate at a fixed distance to measure ball velocity. Asthe ball travels toward the steel plate, it activates each light screenand the ball's time period at each light screen is measured. Thisprovides an incoming transit time period which is inversely proportionalto the ball's incoming velocity. The ball makes impact with the steelplate and rebounds so it passes again through the light screens. As therebounding ball activates each light screen, the ball's time period ateach screen is measured. This provides an outgoing transit time periodwhich is inversely proportional to the ball's outgoing velocity. The CORis then calculates as the ratio of the ball's outgoing transit timeperiod to the ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

Moisture Vapor Transmission Rate (“MVTR”) The preferred standards ofmeasuring the moisture vapor transmission rate include ASTM F1249-90entitled “Standard Test Method for Water Vapor Transmission Rate ThroughPlastic Film and Sheeting Using a Modulated Infrared Sensor,” ASTMF372-94 entitled “Standard Test Method for Water Vapor Transmission Rateof Flexible Barrier Materials Using an Infrared Detection Technique,”and ASTM D-96 entitled “Water Vapor Transmission Rate” among others.

As used herein, the term “about,” used in connection with one or morenumbers or numerical ranges, should be understood to refer to all suchnumbers, including all numbers in a range. It also should be understoodthat when concentrations, amounts, and other numerical data arepresented herein in a range format, they should be interpreted flexiblyto include not only the numerical values explicitly recited as thelimits of the range, but also to include all the individual numericalvalues or sub-ranges encompassed within that range as if each numericalvalue and sub-range is explicitly recited. Furthermore, the inventiondescribed and claimed herein is not to be limited in scope by thespecific embodiments herein disclosed, since these embodiments areintended as illustrations of several aspects of the invention. Anyequivalent embodiments are intended to be within the scope of thisinvention. Indeed, various modifications of the invention in addition tothose shown and described herein will become apparent to those skilledin the art from the foregoing description. Such modifications are alsointended to fall within the scope of the appended claims.

We claim:
 1. A golf ball, comprising: a core having a first Shore Csurface hardness of C₁ in the range of 50 to 90, the core being formedfrom a rubber composition; an intermediate layer surrounding the core,the intermediate layer being formed from a olefin-based acid copolymerionomer composition and having a hardness in the range of 30 to 90 ShoreD; and a cover layer surrounding the intermediate layer having a secondShore C surface hardness of C₂ in the range of 60 to 95, the cover layerbeing formed from a thermoset polyurethane or polyurethane-ureacomposition that is produced by a reaction of: i) an isocyanatecompound, ii) a moisture-resistant polyol having a weight averagemolecular weight in the range of 500 to 10,000 grams per mole, and iii)a curing agent selected from hydroxyl-terminated or amine-terminatedcuring agents, and mixtures thereof, and wherein the ratio of C₂ to C₁is in the range of 0.6 to 1.4, wherein the cover layer has a moisturevapor transmission rate between 3 grams·mm/m²·day to 4 grams·mm/m²·day.2. The golf ball of claim 1, wherein the rubber composition is selectedfrom the group consisting of polybutadiene, polyisoprene, naturalrubber, ethylene-propylene, ethylene-propylene diene, andstyrene-butadiene rubbers, and mixtures thereof.
 3. The golf ball ofclaim 2, wherein the rubber composition is polybutadiene rubber.
 4. Thegolf ball of claim 1, wherein the olefin-based acid copolymer ionomercomposition is an ethylene based acid copolymer.
 5. The golf ball ofclaim 1, wherein the olefin-based add copolymer contains acid groupsselected from the group consisting of methacrylic, acrylic, maleic,crotonic, fumaric, and itaconic add.
 6. The golf ball of claim 5,wherein the olefin-based acid copolymer contains acid groups in anamount of 16 wt. % or less.
 7. The golf ball of claim 5, wherein theolefin-based add copolymer contains acid groups in an amount of greaterthan 16 wt. %.
 8. The golf ball of claim 1, wherein the add groups ofthe olefin-based add copolymer are neutralized to a neutralization levelof 10 to 80%.
 9. The golf ball of claim 5, wherein the add groups of theolefin-based acid copolymer are neutralized to a neutralization level of80 to 100%.
 10. A golf ball, comprising: a core having an inner core andouter core layer, the inner core having a first Shore C surface hardnessof C₁ in the range of 50 to 90, and the outer core layer having a ShoreD surface hardness in the range of about 50 to about 90; an intermediatelayer surrounding the core, the intermediate layer being formed from aolefin-based add copolymer ionomer composition and having a hardness inthe range of 30 to 90 Shore D; and a cover layer surrounding theintermediate layer having a second Shore C surface hardness of C₂ in therange of 60 to 95, the cover layer being formed from a thermosetpolyurethane or polyurethane-urea composition that is produced by areaction of: i) an isocyanate compound, ii) a moisture-resistant polyolhaving a weight average molecular weight in the range of 500 to 10,000grams per mole, and iii) a curing agent selected fromhydroxyl-terminated or amine-terminated curing agents, and mixturesthereof, and wherein the ratio of C₂ to C₁ is in the range of 0.6 to1.4, wherein the cover layer has a moisture vapor transmission ratebetween 3 grams·mm/m²·day to 4 grams·mm/m²·day.